3,508 research outputs found
Magnetization reversal through synchronization with a microwave
Based on the Landau-Lifshitz-Gilbert equation, it can be shown that a
circularly-polarized microwave can reverse the magnetization of a Stoner
particle through synchronization. In comparison with magnetization reversal
induced by a static magnetic field, it can be shown that when a proper
microwave frequency is used the minimal switching field is much smaller than
that of precessional magnetization reversal. A microwave needs only to overcome
the energy dissipation of a Stoner particle in order to reverse magnetization
unlike the conventional method with a static magnetic field where the switching
field must be of the order of magnetic anisotropy.Comment: 4 pages, 5 figure
Zero-field magnetization reversal of two-body Stoner particles with dipolar interaction
Nanomagnetism has recently attracted explosive attention, in particular,
because of the enormous potential applications in information industry, e.g.
new harddisk technology, race-track memory[1], and logic devices[2]. Recent
technological advances[3] allow for the fabrication of single-domain magnetic
nanoparticles (Stoner particles), whose magnetization dynamics have been
extensively studied, both experimentally and theoretically, involving magnetic
fields[4-9] and/or by spin-polarized currents[10-20]. From an industrial point
of view, important issues include lowering the critical switching field ,
and achieving short reversal times. Here we predict a new technological
perspective: can be dramatically lowered (including ) by
appropriately engineering the dipole-dipole interaction (DDI) in a system of
two synchronized Stoner particles. Here, in a modified Stoner-Wohlfarth (SW)
limit, both of the above goals can be achieved. The experimental feasibility of
realizing our proposal is illustrated on the example of cobalt nanoparticles.Comment: 5 pages, 4 figure
Motion of a Vector Particle in a Curved Space-time. IV. Asymptotical shape of caustic
The studies of influence of spin on a photon motion in a Schwartzschild
spacetime is continued. In the previous paper [2] the first order correction to
the geodesic motion is reduced to a non-uniform linear ordinary differential
equation and the equation obtained has been solved by the standard method of
integration of the Green function. If each photon draws a world line specified
by this solution then light rays from infinitely distant source form a caustic
which does not appear without the spin-gravity interaction. The goal of the
present work is to obtain explicit form of caustic.Comment: 6 page
Non-linear effects in the cyclotron resonance of a massless quasi-particle in graphene
We consider the classical motion of a massless quasi-particle in a magnetic
field and under a weak electromagnetic radiation with the frequency .
Due to the non-parabolic, linear energy dispersion, the particle responds not
only at the frequency but generates a broad frequency spectrum around
it. The linewidth of the cyclotron resonance turns out to be very broad even in
a perfectly pure material which allows one to explain recent experimental data
in graphene. It is concluded that the linear response theory does not work in
graphene in finite magnetic fields.Comment: 5 pages, 4 figure
The effect of a velocity barrier on the ballistic transport of Dirac fermions
We propose a novel way to manipulate the transport properties of massless
Dirac fermions by using velocity barriers, defining the region in which the
Fermi velocity, , has a value that differs from the one in the
surrounding background. The idea is based on the fact that when waves travel
accross different media, there are boundary conditions that must be satisfied,
giving rise to Snell's-like laws. We find that the transmission through a
velocity barrier is highly anisotropic, and that perfect transmission always
occurs at normal incidence. When in the barrier is larger that the
velocity outside the barrier, we find that a critical transmission angle
exists, a Brewster-like angle for massless Dirac electrons.Comment: 4.3 pages, 5 figure
Technology as an economic catalyst in rural and depressed places in Massachusetts
This paper uses case studies, including two cities (Lynn and New Bedford), a sub-city district (Roxbury) and two towns in rural Franklin County (Greenfield and Orange), to examine the role of technology as a potential economic catalyst in rural and depressed places in Massachusetts. Though the five target areas vary in size, density, geographic area, demographic characteristics and economic resources, each exhibits chronic patterns of economic distress related to the decline of manufacturing, construction and other key industries
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